The invention relates to a protective switch for use as a breaker or a switch to protect a low-voltage indoor electric line or a device from over-current. More particularly, the invention relates to a tripping device of the protective switch.
Generally, a protective switch of this kind has an over-current tripping device incorporated therein, which acts on a locking member of a switching mechanism upon detection of over-current and releases the locked switching mechanism to cause a breaking action (tripping). Usually, the over-current tripping device carries out time-delay tripping in which an overload current is tripped with lapse of a delay time corresponding to a current value, and carries out instantaneous tripping in which large current such as short-circuit current is tripped instantaneously. An alarm switch may be attached to the protective switch as an auxiliary device. If the protective switch is instantaneously tripped due to a large accidental current, the alarm switch sends an electric signal to warn an external device, and further indicates mechanically on a front surface of the switch.
Examples of a tripping control device for the protective switch include a voltage tripping device and an under-voltage tripping device. The voltage tripping device is used to control the protective switch from a distance, and trips the protective switch when a predetermined voltage is applied thereto. On the other hand, the under-voltage tripping device constantly monitors a circuit voltage, and if the circuit voltage becomes lower than a specified value, the under-voltage tripping device trips the protective switch. An alarm switch and tripping control device are ordinarily mounted on a side of a body of the protective switch.
FIG. 5 is a longitudinal sectional view showing a conventional triple pole protective switch that includes an electromagnetic over-current tripping mechanism with an instantaneous tripping characteristic (hereinafter referred to as xe2x80x9cinstantaneous tripping mechanismxe2x80x9d) and a thermally-actuated over-current tripping mechanism with a time-delay tripping characteristic (hereinafter referred to as xe2x80x9ctime-delay tripping mechanismxe2x80x9d) as over-current tripping devices. In FIG. 5, each of phase circuits housed in a switch body housing 1 is comprised of a pair of fixed contacts 2, 3 and a movable contact 4 that bridges the pair of fixed contacts 2, 3. The movable contact 4 is pressed against the fixed contacts 2, 3 by a contact spring 5 comprised of a compression coil spring inserted between the movable contact 4 and a housing bottom 1a to close the circuit. The movable contact 4 is held by a three-phase integrated movable contact holder 6 formed of an insulating material, and the movable contact holder 6 is movably guided by the housing 1 in a vertical direction with respect to the housing bottom in a vertical direction in FIG. 5.
A power supply-side terminal 7 is integrated with the fixed contact 2, and the fixed contact 3 is connected to a lower end of a bimetal 8a of a time-delay tripping mechanism 8. An upper end of the bimetal 8a is connected to one end of a heater 8b. The heater 8b is wound on the bimetal 8a through an insulating material (not shown) and the other end of the heater 8b is connected to one end of an electromagnetic coil 9a of an instantaneous tripping mechanism 9. The other end of the electromagnetic coil 9a is connected to a load-side terminal 10. The instantaneous tripping mechanism 9 is constructed such that the electromagnetic coil 9a wound around a cylindrical bobbin 9c is positioned vertically with respect to the housing bottom 1a in a U-shaped yoke 9b, and a cylindrical plunger 9d is slidably inserted into the bobbin 9c. An operating member 9e is joined to a head of the plunger 9d, and the plunger 9d forced upward in FIG. 5 by a return spring 9f is fixed with the operating member 9e being in contact with an upper end of the yoke 9b. 
A switching mechanism 11 has a pair of right and left opening and closing levers 13 that rotate around a switching shaft 12. Ends of the levers 13 stay at both sides of the instantaneous tripping mechanism 9 at a central pole and above the movable contact holder 6 in the circuit-closed state as shown in FIG. 5. The switching mechanism 11 is operated by a butterfly-shaped operating handle 14 projecting from the housing 1, and a latch 17 is locked at a latch receiver 26 while the pair of breaking springs 25 formed of a torsion spring is wound.
FIG. 6 is a front view showing a reset state of the switching mechanism 11, taken along line (6)xe2x80x94(6) in FIG. 5, and FIG. 7 is a front view showing a tripping state of the switching mechanism in FIG. 6. The switching mechanism 11 is constructed as an integral unit such that mechanical parts are supported on a frame 15 having front and rear side plates (the front side plate is omitted from FIGS. 6 and 7). The operating handle 14 is supported on the frame 15 such that it is capable of pivoting around a handle shaft 16, and the latch 17 is rotatably supported on the handle shaft 16. An upper end of an upper link 18 is connected to the operating handle 14 via a shaft 19, and an upper end of a lower link 20 is connected to a lower end of the upper link 18 via one end 21a of a U-shaped pin 21. The U-shaped pin 21 has the other end 21b rested on the latch 17 so that the latch 17 locks the upper link 18 and the lower link 20. The upper link 18 and the lower link 20 constitute a toggle link.
A transmission pin 22 is connected to a lower end of the lower link 20, and both ends of the transmission pin 22 are slidably inserted into a slot 23 formed in the side plates of the frame. Another transmission pin 24 is connected to the switching levers 13 such that the pin 24 crosses a transmission pin 16. The pair of switching levers 13 is connected to the switching shaft 12, which has both ends supported on the housing 1, with an interval formed therebetween, and the transmission pin 24 is bridged between the right and left switching levers 13. The switching shaft 12 is rotatably supported on the housing 1, and the pair of breaking springs 25 is fitted into the switching shaft 12 with one end of the breaking spring 25 being engaged with the transmission pin 24 and the other end thereof being engaged with the frame 15. The breaking spring 25 is twisted in an ON state in FIG. 6, and applies a push-up force P from the transmission pin 24 to the transmission pin 22 so as to rotate the switching levers 13 clockwise in FIG. 5.
The push-up force P causes the transmission pin 22 of the lower link 20 to move upward along the slot 23. As a result, the entire lower link 20 tries to rotate counterclockwise in FIG. 6, but is kept in a position shown in FIG. 6 since the U-shaped pin 21 locks the upper end thereof. The lower link applies a tensile force Q to the latch 17 via the U-shaped pin 21. As a result, the latch 17 tries to rotate clockwise in FIG. 6 around the handle shaft 16, but is kept in a position shown in FIG. 6 since it is locked by the latch receiver 26 serving as a locking member.
The latch receiver 26 is a vertically extended plate having a pair of right and left bent arms 26a at a substantially intermediate position thereof, and has a quadrate window hole formed in the plate near the arms 26a. The latch receiver 26 is rotatably supported on the frame 15 via a shaft 27 extending through the arms 26a, and has an engagement portion 26b, positioned at the lower edge of the window hole to engage an L-shaped portion 17a of the latch 17 to lock the latch 17. In response to pressure applied by the latch 17, the latch receiver 26 tries to rotate clockwise in FIG. 6, but is inhibited from rotating and kept in an upright position shown in FIG. 6 since a tongue piece 26c projecting from the latch receiver 26 to the right and left is brought into contact with a side edge of a notch of the frame 15. It should be noted that a return spring 28 formed of a helical compression coil spring is inserted between a lower end of the latch receiver 26 and the frame 15, and the latch receiver 26 is forced clockwise in FIG. 6.
In the circuit-closed state in FIG. 5, current flows from the power supply-side terminal 7 to the load-side terminal 10 via the fixed contact 2, the movable contact 4, the fixed contact 3, the bimetal 8a, the heater 8b, and the electromagnetic coil 9a. When a current flowing through a circuit breaker becomes overloaded with twice or three times higher than a rated current, the bimetal 8a heated by the heater 9b is curved. After a delayed time according to a current value, an operating end portion of the latch receiver 26 rotates counterclockwise in response to a tripping force R in FIG. 6 applied via a transmission mechanism (not shown). This releases the locked switching mechanism 11 to rotate the latch 17 clockwise. As a result, the toggle links 18, 20 are bent, and the switching levers 13 are rotated clockwise in FIG. 5 due to the force of the breaking springs 25. The switching levers 13 push down the movable contact 4 via the movable contact holder 6, and separate the movable contact 4 from the fixed contacts 2, 3 to shut off the current (time-delay tripping action).
FIG. 7 shows the tripping state of the switching mechanism 11. To reset the tripping switching mechanism 11 back to the state in FIG. 6, the operating handle 14 is turned clockwise in FIG. 7. The toggle links 18, 20 are extended to press the U-shaped pin 21 to the right. The latch 17 is lifted counterclockwise around the handle shaft 16 as pivot, and the L-shaped portion 17a of the latch 17 engages the engagement portion 26b of the latch receiver 26 that has been brought into an upright position again by the return spring 28.
On the other hand, when a heavy current (hereinafter referred to as xe2x80x9can instant currentxe2x80x9d) that is twelve to thirteen times larger than a rated current flows through the circuit breaker, the instantaneous tripping mechanism 9 operates to cause instantaneous tripping. Namely, when the heavy current flows through the electromagnetic coil 9a, the plunger 9d is instantaneously pulled against the return spring 9f and releases the latch 17 locked by the latch receiver 28 via a trip member 29 (FIG. 5). And, the protective switch trips (an instantaneous tripping action). The trip member 29 is formed of an insulating plate, and is guided on a groove on the housing 1 along the frame side plate by a side of the instantaneous tripping mechanism of the switching mechanism 11 in FIG. 5 such that the trip member 29 is capable of moving vertically with respect to the bottom of the housing 1.
FIG. 8 is a front view showing the trip member 29. In FIG. 8, plunger operating sections 29a facing ends of the operating member 9e integrated with the plunger 9d of the instantaneous tripping mechanism 9 at each pole are formed at three positions on a top end surface of the trip member 29. A window hole 30, into which the latch receiver 26 is fitted, is formed in the trip member 29, and a locking member (a latch receiver) operating section 29b formed of an inclined face that presses the latch receiver 26 is formed as a part of the peripheral edge of the window hole 30. A tripping section 29c facing an operating member of a tripping control device described later is formed at an upper left shoulder of the trip member 29 in FIG. 8. Further, a U-shaped notch 31 is formed at a right side of the trip member 29 in FIG. 8, and a switch operating section 29d facing an actuator of an alarm switch described later is formed at an upper edge of the notch 31.
FIGS. 9 to 11 are cross-sectional views of the protective switch taken along the trip member 29, wherein FIG. 9 shows the reset state, FIG. 10 shows the tripping state caused by the instant current, and FIG. 11 shows the tripping state caused by the tripping control device. First, in FIG. 9, the trip member 29 is forced by a back spring 32 formed of a compression coil in a direction away from the housing bottom portion 1, then is brought into contact with a stopper (not shown) formed and bent on the frame 15 of the switching mechanism 11. The operating member 9e integrated with the plunger 9d of the instantaneous tripping mechanism 9 is positioned in proximity to the plunger operating sections 29a of the trip member 29 to oppose thereto.
A tripping control device 33 comprised of a voltage tripping device or an under-voltage tripping device is mounted on a left side of the protective switch housing 1, and an operating member 33a that outputs an operation of the tripping control device 33 is positioned in proximity to the tripping section 29c of the trip member 29 to oppose thereto. An alarm switch 34 for transmitting the instantaneous tripping action of the protective switch to an external device via an electric signal is mounted on a right side of the protective switch housing 1, and an actuator 34a of the alarm switch 34 is opposed to the switch operating section 29d of the trip member 29. The actuator 34a is constructed as a lever that is rotatably supported by a shaft 34b, and is urged in the clockwise direction in FIG. 9 by a torsion spring (not shown). An alarm contact (not shown) and an action display rod 34c are provided inside the alarm switch 34, and the action display rod 34c is locked by the actuator 34a in the state shown in FIG. 9 and is held in an embedded state.
When a heavy current such as a short-circuit current flows in the state in FIG. 9, the instantaneous tripping mechanism 9 instantaneously pulls the plunger 9d. As a result, the operating member 9e pushes the trip member 29 down by a stroke S via the plunger operating section 29a, as shown in FIG. 10. The lowered trip member 29 moves the latch receiver 26 to the left in FIG. 9 by means of the latch receiver operating section 29b comprised of an inclined face. The locked switching mechanism 11 is released to cause the protective switch to trip. At the same time, the trip member 29 rotates the actuator 34a of the alarm switch 34 via the switch operating section 9d. The alarm contacts are switched to transmit a trip signal, and the display rod 34c is pushed by a spring (not shown) to project from the alarm switch 34 to indicate an occurrence of the instantaneous tripping.
In the state shown in FIG. 9, when the tripping control device 33 operates in response to an input of a tripping instruction to the voltage tripping device or to a drop in the circuit voltage by the under-voltage tripping device, the operating member 33a moves downward in FIG. 9 to push down the trip member 29 via the tripping section 29c. Accordingly, the latch receiver 26 moves and trips the protective switch. In the reset state in FIG. 9, there is a gap G between the switch operating section 29d of the trip member 29 and the actuator 34a of the alarm switch 34, and a downward stroke s (FIG. 11) during the operation of the tripping control device 33 is set to be smaller than the gap G (s less than G less than S). Therefore, during the operation of the tripping control device 33, the switch operating section 29d of the lowered trip member 29 can not reach the actuator 34a, and does not operate the alarm switch 34. Namely, the tripping action by the tripping control device 33 and the instantaneous tripping action by the instantaneous tripping mechanism 9 are separated from each other, and the alarm switch 34 is operated only during the instantaneous tripping action.
Conventionally, in the reset state (FIG. 9), the gap G is provided between the switch operating section 29d of the trip member 29 and the actuator 34a of the alarm switch 34, and the operational stroke s of the tripping control device 33 is set to be smaller than the gap G, so that the alarm switch 34 can be operated only during the instantaneous tripping action. There is no problem with this structure in the case where an instant current is as large as a short circuit current. However, an absorption stroke of the plunger 9d might become smaller than the gap G in a range near the lower limit of an operational current value of the instantaneous tripping mechanism 9, and if it is the case, the alarm switch 34 can not be operated even during the instantaneous tripping action. It is difficult to perfectly adjust the absorption stroke S of the plunger 9d, the operational stroke s of the tripping control device 33, and the gap G in order to solve the above-mentioned problem because there is a variation in operational characteristics and dimensional accuracy of the parts.
It is therefore an object of the present invention to provide a protective switch that is capable of inhibiting an alarm switch from operating during a tripping caused by a tripping control device, and surely operating the alarm switch in an entire range of an instant current.
Further objects and advantages will be apparent from the following description of the invention.
To attain the above objects, in a protective switch of the invention, a trip member is divided into an upper trip member away from a bottom of a housing and a lower trip member close to the bottom of the housing. The lower trip member is urged by a back spring, and the upper trip member is formed of a plunger operating section opposed to an operating member of a plunger and a switch operating section opposed to an actuator of an alarm switch. The lower trip member is formed of a locking member operating section opposed to a locking member of a switching mechanism and a tripping section opposed to an operating member of a tripping control device.
According to the present invention, the tripping control device is capable of tripping the protective switch by moving only the lower trip member independently from the upper trip member that operates the alarm switch. Accordingly, a gap between the switch operating section of the upper trip member and the actuator of the alarm switch can be minimized, regardless of an operational stroke of the tripping control device. Thus, it is possible to operate the alarm switch in an entire range of an instant current. When the instant current flows, the operating member of the plunger moves the upper trip member to push down the lower trip member and move the locking member of the switching mechanism, thus causing instantaneous tripping.